The present invention relates to molybdenum or tungsten particles having a stable face-centered cubic structure of molybdenum and tungsten belonging to a VI group in a periodic table or a thin film formed from the foregoing particles, and a manufacturing method thereof.
Molybdenum and tungsten belonging to a VI group in a periodic table is a high-melting material that is used as an electrode material or the like, and there are four known types of crystal structures thereof, namely, amorphous, body-centered cubic (bcc) structure, hexagonal close-packed (hcp) structure, and face-centered cubic (fcc) structure. Among the foregoing crystal structures, the bcc structure is a thermodynamically stable structure. Contrarily, the hcp or fcc structure is a thermodynamically metastable structure. If the molybdenum and tungsten of the bcc structure are subject to high-temperature and high-pressure treatment, they will be subject to phase transformation and synthesis in the order of bcc→hcp→fcc (refer to Non-Patent Documents 1 and 2).
Meanwhile, in the field of cluster science that deals with clusters in the size of several nanometers, stable crystal structures are being discussed from the perspective of surface energy. With clusters having a size of 4 nm or greater, the bcc structure or the A15 structure, which is a slightly distorted version of the bcc structure, is stable. If the size of clusters becomes less than 4 nm, the surface stability caused by the reduction in surface energy is to be the driving force and the fcc structure will appear. An example where a molybdenum plate was sputtered and synthesized in a chamber, which was filled with argon gas and adjusted so that the pressure was to be 0.1 mbar or less, has been reported (refer to Non-Patent Document 3).
Elements having the fcc structure are known to create nanoparticles having crystallographically five-fold symmetry. For example, with elements such as gold, silver, copper, germanium and silicon, in which the thermodynamically stable structure is an fcc structure, numerous nanoparticles having five-fold symmetry such as decahedron or icosahedron have been observed in the nanoparticles created during the process of evaporating and condensing the ingots of the foregoing elements (refer 10 to Non-Patent Document 4). This is based on the fact that the basic structure of a pentagonal substance is an fcc structure. Five units having an fcc structure are arranged around a single axis (five-fold symmetrical axis), and it results in the formation of a pentagonal structure.
In recent years, the synthesis of nanorods in which gold, silver and copper decahedrons grow in a one-dimensional direction along the five-fold symmetrical axis has also been reported (refer to Non-Patent Documents 5 to 7). Meanwhile, since the thermodynamically stable structure of molybdenum and tungsten belonging to the VI group in a periodic table is a bcc structure as described above, the creation of a pentagonal substance has not been reported thus far.    [Non-Patent Document 1] J. Phys.: Condense Matter 17, 1049-1057, (2005)    [Non-Patent Document 2] Physical Review B, 52, 9121-9124 (1994)    [Non-Patent Document 3] Appl. Phys. Lett, 86, 113113 (2005)    [Non-Patent Document 4] Encyclopedia of Nanoscience and Nanotechnology, Volume X, 1-22 (2003)    [Non-Patent Document 5] Physical Review B, 61, 4968-4874 (2000)    [Non-Patent Document 6] J. Mater. Chem, 12, 1765-1770 (2002)    [Non-Patent Document 7] Nano Letters, 3, 955-960 (2003)